Final answer:
Irving, who is 78 years old, takes human growth hormone supplements to regain the strength of his youth. He may be disappointed, because the hormone has been shown only to increase muscle mass. The correct option is 3.
Step-by-step explanation:
Human growth hormone (hGH) primarily promotes the synthesis of protein in skeletal muscle and bones, activating Insulin-like growth factor 1 (IGF-1), which further supports the formation of new proteins. While hGH might help with muscle regeneration post-exercise, its effects on reversing the aging process or improving cognitive function are not supported by scientific evidence.
Studies indicate that exercise and healthy lifestyle choices can more effectively slow down the aging process than growth hormone supplementation itself. Hence, 3 is the correct option.